/*
    Copyright (C) 2012-2013 de4dot@gmail.com

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

﻿using System;
using System.Collections.Generic;
using System.IO;
using dnlib.DotNet.Emit;

namespace dnlib.DotNet.Writer {
	/// <summary>
	/// Returns tokens of token types, strings and signatures
	/// </summary>
	public interface ITokenCreator {
		/// <summary>
		/// Gets the token of <paramref name="o"/>
		/// </summary>
		/// <param name="o">A token type or a string or a signature</param>
		/// <returns>The token</returns>
		MDToken GetToken(object o);

		/// <summary>
		/// Gets a <c>StandAloneSig</c> token
		/// </summary>
		/// <param name="locals">All locals</param>
		/// <param name="origToken">The original token or <c>0</c> if none</param>
		/// <returns>A <c>StandAloneSig</c> token or <c>0</c> if <paramref name="locals"/> is
		/// empty.</returns>
		MDToken GetToken(IList<TypeSig> locals, uint origToken);

		/// <summary>
		/// Called when an error is detected (eg. a null pointer). The error can be
		/// ignored but the method won't be valid.
		/// </summary>
		/// <param name="message">Error message</param>
		void Error(string message);
	}

	/// <summary>
	/// Writes CIL method bodies
	/// </summary>
	public sealed class MethodBodyWriter : MethodBodyWriterBase {
		ITokenCreator helper;
		CilBody cilBody;
		bool keepMaxStack;
		uint codeSize;
		uint maxStack;
		byte[] code;
		byte[] extraSections;

		/// <summary>
		/// Gets the code as a byte array. This is valid only after calling <see cref="Write()"/>.
		/// The size of this array is not necessarily a multiple of 4, even if there are exception
		/// handlers present. See also <see cref="GetFullMethodBody()"/>
		/// </summary>
		public byte[] Code {
			get { return code; }
		}

		/// <summary>
		/// Gets the extra sections (exception handlers) as a byte array or <c>null</c> if there
		/// are no exception handlers. This is valid only after calling <see cref="Write()"/>
		/// </summary>
		public byte[] ExtraSections {
			get { return extraSections; }
		}

		/// <summary>
		/// Constructor
		/// </summary>
		/// <param name="helper">Helps this instance</param>
		/// <param name="cilBody">The CIL method body</param>
		public MethodBodyWriter(ITokenCreator helper, CilBody cilBody)
			: this(helper, cilBody, false) {
		}

		/// <summary>
		/// Constructor
		/// </summary>
		/// <param name="helper">Helps this instance</param>
		/// <param name="cilBody">The CIL method body</param>
		/// <param name="keepMaxStack">Keep the original max stack value that has been initialized
		/// in <paramref name="cilBody"/></param>
		public MethodBodyWriter(ITokenCreator helper, CilBody cilBody, bool keepMaxStack)
			: base(cilBody.Instructions, cilBody.ExceptionHandlers) {
			this.helper = helper;
			this.cilBody = cilBody;
			this.keepMaxStack = keepMaxStack;
		}

		/// <summary>
		/// Writes the method body
		/// </summary>
		public void Write() {
			codeSize = InitializeInstructionOffsets();
			maxStack = keepMaxStack ? cilBody.MaxStack : GetMaxStack();
			if (NeedFatHeader())
				WriteFatHeader();
			else
				WriteTinyHeader();
			if (exceptionHandlers.Count > 0)
				WriteExceptionHandlers();
		}

		/// <summary>
		/// Gets the code and (possible) exception handlers in one array. The exception handlers
		/// are 4-byte aligned.
		/// </summary>
		/// <returns>The code and any exception handlers</returns>
		public byte[] GetFullMethodBody() {
			int padding = Utils.AlignUp(code.Length, 4) - code.Length;
			var bytes = new byte[code.Length + (extraSections == null ? 0 : padding + extraSections.Length)];
			Array.Copy(code, 0, bytes, 0, code.Length);
			if (extraSections != null)
				Array.Copy(extraSections, 0, bytes, code.Length + padding, extraSections.Length);
			return bytes;
		}

		bool NeedFatHeader() {
			//TODO: If locals has cust attrs, we also need a fat header
			return codeSize > 0x3F ||
					exceptionHandlers.Count > 0 ||
					cilBody.HasVariables ||
					maxStack > 8;
		}

		void WriteFatHeader() {
			if (maxStack > ushort.MaxValue) {
				Error("MaxStack is too big");
				maxStack = ushort.MaxValue;
			}

			ushort flags = 0x3003;
			if (exceptionHandlers.Count > 0)
				flags |= 8;
			if (cilBody.InitLocals)
				flags |= 0x10;

			code = new byte[12 + codeSize];
			var writer = new BinaryWriter(new MemoryStream(code));
			writer.Write(flags);
			writer.Write((ushort)maxStack);
			writer.Write(codeSize);
			writer.Write(helper.GetToken(GetLocals(), cilBody.LocalVarSigTok).Raw);
			if (WriteInstructions(writer) != codeSize)
				Error("Didn't write all code bytes");
		}

		IList<TypeSig> GetLocals() {
			var localsSig = new TypeSig[cilBody.Variables.Count];
			for (int i = 0; i < cilBody.Variables.Count; i++)
				localsSig[i] = cilBody.Variables[i].Type;
			return localsSig;
		}

		void WriteTinyHeader() {
			code = new byte[1 + codeSize];
			var writer = new BinaryWriter(new MemoryStream(code));
			writer.Write((byte)((codeSize << 2) | 2));
			if (WriteInstructions(writer) != codeSize)
				Error("Didn't write all code bytes");
		}

		void WriteExceptionHandlers() {
			var outStream = new MemoryStream();
			var writer = new BinaryWriter(outStream);
			if (NeedFatExceptionClauses())
				WriteFatExceptionClauses(writer);
			else
				WriteSmallExceptionClauses(writer);
			extraSections = outStream.ToArray();
		}

		bool NeedFatExceptionClauses() {
			// Size must fit in a byte, and since one small exception record is 12 bytes
			// and header is 4 bytes: x*12+4 <= 255 ==> x <= 20
			if (exceptionHandlers.Count > 20)
				return true;

			foreach (var eh in exceptionHandlers) {
				if (!FitsInSmallExceptionClause(eh.TryStart, eh.TryEnd))
					return true;
				if (!FitsInSmallExceptionClause(eh.HandlerStart, eh.HandlerEnd))
					return true;
			}

			return false;
		}

		bool FitsInSmallExceptionClause(Instruction start, Instruction end) {
			uint offs1 = GetOffset2(start);
			uint offs2 = GetOffset2(end);
			if (offs2 < offs1)
				return false;
			return offs1 <= ushort.MaxValue && offs2 - offs1 <= byte.MaxValue;
		}

		uint GetOffset2(Instruction instr) {
			if (instr == null)
				return codeSize;
			return GetOffset(instr);
		}

		void WriteFatExceptionClauses(BinaryWriter writer) {
			const int maxExceptionHandlers = (0x00FFFFFF - 4) / 24;
			int numExceptionHandlers = exceptionHandlers.Count;
			if (numExceptionHandlers > maxExceptionHandlers) {
				Error("Too many exception handlers");
				numExceptionHandlers = maxExceptionHandlers;
			}

			writer.Write((((uint)numExceptionHandlers * 24 + 4) << 8) | 0x41);
			for (int i = 0; i < numExceptionHandlers; i++) {
				var eh = exceptionHandlers[i];
				uint offs1, offs2;

				writer.Write((uint)eh.HandlerType);

				offs1 = GetOffset2(eh.TryStart);
				offs2 = GetOffset2(eh.TryEnd);
				if (offs2 <= offs1)
					Error("Exception handler: TryEnd <= TryStart");
				writer.Write(offs1);
				writer.Write(offs2 - offs1);

				offs1 = GetOffset2(eh.HandlerStart);
				offs2 = GetOffset2(eh.HandlerEnd);
				if (offs2 <= offs1)
					Error("Exception handler: HandlerEnd <= HandlerStart");
				writer.Write(offs1);
				writer.Write(offs2 - offs1);

				if (eh.HandlerType == ExceptionHandlerType.Catch)
					writer.Write(helper.GetToken(eh.CatchType).Raw);
				else if (eh.HandlerType == ExceptionHandlerType.Filter)
					writer.Write(GetOffset2(eh.FilterStart));
				else
					writer.Write(0);
			}
		}

		void WriteSmallExceptionClauses(BinaryWriter writer) {
			const int maxExceptionHandlers = (0xFF - 4) / 12;
			int numExceptionHandlers = exceptionHandlers.Count;
			if (numExceptionHandlers > maxExceptionHandlers) {
				Error("Too many exception handlers");
				numExceptionHandlers = maxExceptionHandlers;
			}

			writer.Write((((uint)numExceptionHandlers * 12 + 4) << 8) | 1);
			for (int i = 0; i < numExceptionHandlers; i++) {
				var eh = exceptionHandlers[i];
				uint offs1, offs2;

				writer.Write((ushort)eh.HandlerType);

				offs1 = GetOffset2(eh.TryStart);
				offs2 = GetOffset2(eh.TryEnd);
				if (offs2 <= offs1)
					Error("Exception handler: TryEnd <= TryStart");
				writer.Write((ushort)offs1);
				writer.Write((byte)(offs2 - offs1));

				offs1 = GetOffset2(eh.HandlerStart);
				offs2 = GetOffset2(eh.HandlerEnd);
				if (offs2 <= offs1)
					Error("Exception handler: HandlerEnd <= HandlerStart");
				writer.Write((ushort)offs1);
				writer.Write((byte)(offs2 - offs1));

				if (eh.HandlerType == ExceptionHandlerType.Catch)
					writer.Write(helper.GetToken(eh.CatchType).Raw);
				else if (eh.HandlerType == ExceptionHandlerType.Filter)
					writer.Write(GetOffset2(eh.FilterStart));
				else
					writer.Write(0);
			}
		}

		/// <inheritdoc/>
		protected override void ErrorImpl(string message) {
			helper.Error(message);
		}

		/// <inheritdoc/>
		protected override void WriteInlineField(BinaryWriter writer, Instruction instr) {
			writer.Write(helper.GetToken(instr.Operand).Raw);
		}

		/// <inheritdoc/>
		protected override void WriteInlineMethod(BinaryWriter writer, Instruction instr) {
			writer.Write(helper.GetToken(instr.Operand).Raw);
		}

		/// <inheritdoc/>
		protected override void WriteInlineSig(BinaryWriter writer, Instruction instr) {
			writer.Write(helper.GetToken(instr.Operand).Raw);
		}

		/// <inheritdoc/>
		protected override void WriteInlineString(BinaryWriter writer, Instruction instr) {
			writer.Write(helper.GetToken(instr.Operand).Raw);
		}

		/// <inheritdoc/>
		protected override void WriteInlineTok(BinaryWriter writer, Instruction instr) {
			writer.Write(helper.GetToken(instr.Operand).Raw);
		}

		/// <inheritdoc/>
		protected override void WriteInlineType(BinaryWriter writer, Instruction instr) {
			writer.Write(helper.GetToken(instr.Operand).Raw);
		}
	}
}
